Positive active material, method for preparing same, positive electrode plate containing same, secondary battery, and electrical device

Abstract

This application provides a positive active material. The positive active material is a composite of NaxRy(PO4)z(P2O7)k and C, where 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, or Pb; and a water content of the positive active material is not higher than 1600 ppm. This application further provides a method for preparing the positive active material, a positive electrode plate containing the material, a secondary battery, and an electrical device. The positive active material of this application contains a relatively low water content.

What is claimed is: 
     
         1 . A positive active material, wherein the positive active material is a composite of Na x R y (PO 4 ) z (P 2 O 7 ) k  and C, wherein 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4, and R comprises at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, or Pb; and a water content of the positive active material is not higher than 1600 ppm. 
     
     
         2 . The positive active material according to  claim 1 , wherein the water content is not higher than 1400 ppm, optionally not higher than 1200 ppm, optionally not higher than 1000 ppm, optionally not higher than 900 ppm, optionally not lower than 50 ppm, further optionally not lower than 70 ppm, and still further optionally is 200 to 800 ppm. 
     
     
         3 . The positive active material according to  claim 1 , wherein a chemical composition of the positive active material satisfies at least one of the following conditions:
   3≤x≤5;  (1)
     2≤y≤4;  (2)
     1.5≤z≤2;  (3)
     1≤k≤1.5; or  (4)
     R is Fe.  (5)
   
     
     
         4 . A method for preparing a positive active material, wherein the positive active material is a composite of Na x R y (PO 4 ) z (P 2 O 7 ) k  and C, wherein 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4, and R comprises at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, or Pb; a water content of the positive active material is not higher than 1600 ppm; and the method comprises the following steps:
 a) preparing a precursor material: preparing a mixed slurry containing an R source compound, a sodium source compound, a phosphorus source compound, and a carbon source compound, and drying the mixed slurry to obtain the precursor material; 
 b) sintering the precursor material in a sintering atmosphere to obtain the positive active material, wherein a ratio of a ventilation volume value of a sintering atmosphere to a mass value of the precursor material is 0.85 to 3.42 m 3 /kg, optionally 1.70 to 3.42 m 3 /kg, and further optionally 2.27 to 3.42 m 3 /kg. 
 
     
     
         5 . The method according to  claim 4 , wherein, in step b), a heating rate is 0.5 to 5° C./min, and optionally 2 to 5° C./min. 
     
     
         6 . The method according to  claim 4 , wherein, in step b), the sintering atmosphere comprises nitrogen and/or argon. 
     
     
         7 . The method according to  claim 6 , wherein, in step b), a flow rate of the nitrogen is 2 to 10.5 L/min, optionally 5 to 10.5 L/min; and/or, the sintering continues for a duration of approximately 10 to 30 hours, and optionally approximately 18 to 23 hours. 
     
     
         8 . The method according to  claim 4 , further comprising the following step:
 c) pulverizing the positive active material, wherein the pulverization is performed at an ambient humidity not higher than 10%, and optionally at an ambient humidity of 2% to 10%.   
     
     
         9 . The method according to  claim 4 , further comprising the following step:
 d) oven-drying the positive active material.   
     
     
         10 . A positive electrode plate, comprising the positive active material according to  claim 1 . 
     
     
         11 . A secondary battery, comprising the positive electrode plate according to  claim 10 . 
     
     
         12 . An electrical device, comprising the secondary battery according to  claim 11 .